Methods for manufacturing integrated circuit devices having features with reduced edge curvature

ABSTRACT

A structure, such as an integrated circuit device, is described that includes a line of material with critical dimensions which vary within a distribution substantially less than that of a mask element, such as a patterned resist element, used in etching the line. Techniques are described for processing a line of crystalline phase material which has already been etched using the mask element, in a manner which straightens an etched sidewall surface of the line. The straightened sidewall surface does not carry the sidewall surface variations introduced by photolithographic processes, or other patterning processes, involved in forming the mask element and etching the line.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. ProvisionalApplication No. 61/532,475 entitled “Crystal Self-Assembly Applied toFeature Patterning” filed 8 Sep. 2011, which is incorporated byreference herein.

U.S. application Ser. No. 13/190,319 entitled “Integrated CircuitDevices having Features with Reduced Edge Curvature and Methods forManufacturing the Same” filed 25 Jul. 2011, is incorporated by referenceherein.

BACKGROUND

1. Field of the Invention

The present invention relates to integrated circuit fabrication, andmore particularly to methods for fabricating high-density integratedcircuit devices.

2. Description of Related Art

Photolithographic processes can be used to form a variety of integratedcircuit structures on a semiconductor wafer. In photolithography,features of these structures are typically created by exposing a maskpattern (or reticle) to project an image onto a wafer that is coatedwith light sensitive material such as photo resist. After exposure, thepattern formed in the photo resist may then be transferred to anunderlying layer (e.g. metal, polysilicon, etc.) through etching,thereby creating the desired features.

One problem associated with manufacturing devices having very smallfeatures arises because of variations introduced by thephotolithographic processes. Specifically, resist material properties,process conditions, optical distortions and other factors can causesystematic and random deviations in the etched shapes of the featuresfrom their desired shapes. Examples of deviations includecorner-rounding, line-shortening and line edge roughness.

In a typical lithographic patterning process, a line of resist is usedas an etch mask to create a corresponding line of material in theunderlying layer. In such a case, the deviations in the patterned lineof resist will be transferred to the critical dimensions of the etchedline in the underlying layer. As process technologies continue toshrink, these deviations become a greater percentage of the criticaldimension of the etched lines, which can reduce yield and result insignificant performance variability in devices such as transistorsimplemented utilizing these etched lines.

Accordingly, it is desirable to provide high-density structures such asintegrated circuit devices which overcome or alleviate issues caused bydeviations introduced by photolithographic processes, thereby improvingperformance and manufacturing yield of such devices.

SUMMARY

A structure, such as an integrated circuit device, is described thatincludes a line of material with critical dimensions which vary within adistribution substantially less than that of a mask element, such as apatterned resist element, used in etching the line. Techniques aredescribed for processing a line of crystalline phase material which hasalready been etched using the mask element by utilizing anisotropicproperties of the material, in a manner which straightens an etchedsidewall surface of the line. The straightened sidewall surface does notcarry the sidewall surface variations introduced by photolithographicprocesses, or other patterning processes, involved in forming the maskelement and etching the line.

In one embodiment, the etched sidewall surface of the line extends alonga surface generally parallel to a particular crystal plane of thelayer's crystal lattice which has a relatively slow epitaxial growthrate. The etched sidewall surface is then straightened by performing anepitaxial process to grow crystalline phase material at energeticallyfavorable step or kink sites which define the roughness of the etchedsidewall surface. During the epitaxial growth process, atoms are morelikely to bond at these energetically favorable sites, as compared to analready flat crystal surface along the particular crystal plane. Thistends to advance crystalline growth along the particular plane, which inturn causes the straightening of the sidewall surface.

In another embodiment, the etched sidewall surface of the line extendsalong a surface generally parallel to a particular crystal plane of thelayer's crystal lattice which has a relatively slow etch rate for asubsequent etching process. The etched sidewall surface is thenstraightened by performing the subsequent etching process. During thesubsequent etching process, atoms are more rapidly removed at step orkink sites which define the roughness of the etched sidewall surface, ascompared to removal of atoms on an already flat crystal surface alongthe particular crystal plane. This in turn causes the straightening ofthe sidewall surface along the particular crystal plane.

As a result of these techniques, the variation in the straightenedsidewall surface can be controlled much tighter than the variation inthe sidewall surface of the mask element used in etching the line. Thisresults in the line of material having improved line definition, withstraighter edges and sharper corners, than can be obtained usingconventional lithographic etch mask techniques. In embodiments of thetechnology described herein, the line edge roughness of the straightenedline of material is less than or equal to 1 nm, which is much less thanis possible utilizing conventional techniques.

The above summary of the invention is provided in order to provide abasic understanding of some aspects of the invention. This summary isnot intended to identify key or critical elements of the invention or todelineate the scope of the invention. Its sole purpose is to presentsome concepts of the invention in a simplified form as a prelude to themore detailed description that is presented later. Other aspects andadvantages of the present invention can be seen on review of thedrawings, the detailed description, and the claims which follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-4 illustrate stages in a manufacturing process flow of anembodiment for straightening an etched sidewall surface of a line ofcrystalline phase material.

FIGS. 5A-5F illustrate an example of the epitaxial growth process forstraightening the etched sidewall surface of a line through depositionof material at energetically favorable step or kink sites of thesidewall surface.

FIGS. 6A-6J illustrate example simulations of the epitaxial growthprocess.

FIG. 7 illustrates an example simulation of the epitaxial growth processfor various surfaces along different planes of a crystal lattice for amaterial having a diamond cubic crystal structure.

FIGS. 8-9 illustrate stages in a manufacturing process flow of a secondembodiment for straightening an etched sidewall surface of a line ofcrystalline phase material.

DETAILED DESCRIPTION

The following description is presented to enable any person skilled inthe art to make and use the invention, and is provided in the context ofa particular application and its requirements. Various modifications tothe disclosed embodiment will be readily apparent to those skilled inthe art, and the general principles defined herein may be applied toother embodiments and applications without departing from the spirit andscope of the present invention. Thus, the present invention is notintended to be limited to the embodiments shown, but is to be accordedwith the widest scope consistent with the principles and featuresdisclosed herein.

FIGS. 1-4 illustrate stages in a manufacturing process flow of anembodiment for straightening an etched sidewall surface of a line ofcrystalline phase material. It will be understood that the process stepsand structures described with reference to FIGS. 1-4 do not describe acomplete process for the manufacturing of an integrated circuit device.The processes described herein can be utilized in the manufacturing ofvarious types of integrated circuit components.

FIGS. 1A and 1B (collectively “FIG. 1”) illustrate top andcross-sectional views respectively of a mask element 100 patterned on amaterial layer 110. The mask element 100 has a sidewall surface 102 anda sidewall surface 104. The mask element 100 may be formed by patterninga layer of photoresist using a lithographic process. For example, themask element 100 may be formed for example using 193 nm lithography,extreme ultraviolet (EUV) radiation, electron beams, nanoimprintlithography, spacer lithography, or double patterning. Alternatively,other materials and patterning processes may be used to form the maskelement 100.

The material layer 110 is a layer of crystalline phase material. Asdescribed in more detail below, the material layer 110 is a materialwith a crystal lattice having at least one crystal plane which has arelatively slow epitaxial growth rate. The material layer 110 may forexample comprise silicon or other semiconductor material. Alternatively,the material layer 110 may comprise other materials. In someembodiments, the material layer 110 may be an intermediate layer betweenan underlying layer and the mask element 100.

The mask element 100 has variations in shape as a result ofimperfections and pattern fidelity limitations during the formation ofthe mask element 100. The dashed lines 101, 103 in the top view of FIG.1A represent an idealized shape of the mask element 100. The term “lineedge roughness” (LER) refers to a statistical measure, such as thestandard deviation, of the actual positions of a sidewall surfacerelative to the mean sidewall surface position along the length of asegment of the sidewall surface. The values of LER described hereinrefer to a three-sigma standard deviation of the roughness of thesidewall surface, unless indicated otherwise. The term “line widthroughness” (LWR) refers to a statistical measure, such as the standarddeviation, of the actual line width relative to the mean line widthalong the length of a segment of a line having two sidewall surfaces.The values of LWR described herein refer to a three-sigma standarddeviation of the roughness of the width, unless indicated otherwise.

As can be seen in FIGS. 1A and 1B, the first sidewall surface 102 andthe second sidewall surface 104 each have a pronounced LER. Accordingly,the mask element 100 has a pronounced LWR.

Next, an etching process is performed on the structure illustrated inFIGS. 1A and 1B using the mask element 100 as an etch mask, resulting inthe structure illustrated in the top and cross sectional views of FIGS.2A and 2B (collectively “FIG. 2”). The etch process used depends on thematerial of the material layer 110, and can vary from embodiment toembodiment. In one embodiment in which the material layer 110 issilicon, the etching process is performed using reactive ion etching.

The etching process forms an etched sidewall surface 202 in the materiallayer 110 at a location defined by the sidewall surface 102 of the maskelement 100. Similarly, the etching process forms an etched sidewallsurface 204 in the material layer 110 at a location defined by thesidewall surface 104 of the mask element 100. The sidewall surface 202and the sidewall surface 204 define opposing sides of a line 250 ofcrystalline phase material in the material layer 110.

As shown in FIGS. 2A and 2B, the variation in the respective sidewallsurfaces 102, 104 of the mask element 100 are carried through to thesidewall surfaces 202, 204 in the material layer 110. Due toundercutting by the etching process, the sidewall surfaces 202, 204 eachextend a distance beneath the mask element 100 to define the line 250.

Next, the mask element 100 is removed, resulting in the structureillustrated in the top and cross-sectional views of FIGS. 3A and 3B(collectively “FIG. 3”).

An epitaxial process is then performed on the structure illustrated inFIGS. 3A and 3B to grow additional crystalline phase material on thematerial layer 110, resulting in the structure illustrated in the topand cross-sectional views of FIGS. 4A and 4B (collectively “FIG. 4”). Inthe illustrated example, the additional crystalline phase material thatis grown is the same material as that of the material layer 110. Forexample, in one embodiment, the material layer 110 is silicon, and theadditional material that is grown is also silicon.

Alternatively, the additional crystalline phase material that is grownis different than the material of the material layer 110. For example,in one embodiment, the material layer 110 is silicon, and the additionalmaterial that is grown is germanium. The additional crystalline phasematerial may have the same type of crystal lattice structure as thematerial of the material layer 110, or it may be different.

The epitaxial process and the corresponding process parameters can varyfrom embodiment to embodiment. In some embodiments, the epitaxialprocess is carried out using solid-phase epitaxy (SPE), vapor-phaseepitaxy (VPE), molecular-beam epitaxy (MBE) or liquid-phase epitaxy(LPE).

The material layer 110 serves as a template for crystal growth duringthe epitaxial process. As a result, in embodiments in which theadditional crystalline phase material has the same type of crystallattice structure as the material of the material layer 110, regions ofthe epitaxial layer have the same crystallographic orientation as thecorresponding surfaces of the material layer 110 on which the regionsare grown.

The epitaxial process forms an epitaxial region 420 of crystalline phasematerial on the etched sidewall surface 202 of the line of material 150.As described in more detail below with respect to FIGS. 5, 6 and 7, theepitaxial region 420 acts to straighten the etched sidewall surface 202along a surface parallel to a plane of the crystal lattice of thematerial layer 110, thereby defining a straightened sidewall surface402. This straightening occurs through crystalline growth of theepitaxial region 420 at energetically favorable step or kink sites whichdefine the roughness of the etched sidewall surface 202. During theepitaxial process, atoms are more likely to bond at these energeticallyfavorable sites, as compared to atoms on an already flat crystal surfacealong the particular crystal plane. This tends to advance crystallinegrowth along the particular plane, which in turn causes thestraightening of the sidewall surface 402. The straightening depends onthe duration of the epitaxial process, as well as which plane of thecrystal lattice the straightened sidewall surface 402 extends along. Inembodiments, the crystal orientation of the surface 402 is selected suchthat its epitaxial growth rate is slower than the growth rates of allother crystal orientations. In such a case, parts of the surface thatdeviate from the straight surface will grow faster than the alreadystraight parts of the surface, effectively providing negative feedbackand self-straightening of the surface.

As shown in FIGS. 4A and 4B, the variation in the straightened sidewallsurface 402 is much less than the variation in the etched sidewallsurface 202, and thus much less than the variation in the sidewallsurface 102 of the mask element 100. In other words, the straightenedsidewall surface 402 is much straighter than the sidewall surface 102 ofthe mask element 100 from which the straightened sidewall surface 402originated.

The epitaxial process also forms an epitaxial region 430 of crystallinephase material on the etched sidewall surface 204 of the line ofmaterial 150. Similar to the discussion above, the epitaxial region 430acts to straighten the etched sidewall surface 204, thereby defining astraightened sidewall surface 404. As a result, the straightenedsidewall surface 404 is much straighter than the sidewall surface 104 ofthe mask element 100 from which the straightened sidewall surface 404originated.

Although not illustrated, the epitaxial process will also generally formepitaxial regions on the top surface of the etched line 250, as well asthe top surfaces of the material layer 110 adjacent the sidewallsurfaces 202, 204. If desired, this can be prevented by covering thehorizontal surfaces with an amorphous mask such as an oxide or nitrideand performing selective epitaxy, where polycrystalline material formedon the amorphous surface is removed during the epitaxy.

The straightened sidewall surface 402 and the straightened sidewallsurface 404 define opposing sides of a line 440 of crystalline phasematerial. The line 440 has a line width 445. The line width 445 may befor example 15 nm, or less.

As a result of the straightening during the epitaxial process, thevariation in the straightened sidewall surfaces 402, 404 of the line 440can be controlled over a distribution much less than the variation inthe sidewall surfaces 102, 104 of the mask element 100. These smallvariations arise because the straightened sidewall surfaces 402, 404have variations dependent upon the straightening through crystallinegrowth at energetically favorable atomic step or kink sites, which canbe readily controlled. As a result, these variations in the straightenedsidewall surfaces 402, 404 can be controlled over a distribution muchless than the variations due to photolithographic processes, or otherpatterning processes, involved in the formation of the sidewall surfaces102, 104 of the mask element 100. This results in the line 440 havingimproved line definition, with straighter sidewall surfaces 402, 404,than is possible using conventional techniques. Therefore, integratedcircuit elements, such as FinFET transistors, interconnect lines, memorycells, or other small features such as nano-wires, implemented using theline 440 will exhibit uniform performance and high yield in a way notpossible in the prior art.

As an example, using a lithographic process, the LER of the sidewallsurface 102 and the sidewall surface 104 of the mask element 100 can begreater than 4 nm. As explained above, variations in the straightenedsidewall surfaces 402, 404 of the line 440 are substantially less thanthat of the variations in the sidewall surfaces 102, 104. As a result,the LER of the straightened sidewall surfaces 402, 404 is much smaller,such as for example less than or equal to 1 nm. This results in thewidth 445 of the line 440 having a LWR substantially less than that ofthe mask element 100, such as for example less than or equal to 1.5 nm.

In some embodiments the sidewall surfaces 402, 404 vary by +/− theatomic step size of the material of the epitaxial regions 420, 430. Inone embodiment in which the epitaxial regions 420, 430 are silicon, thevariation is the atomic step size of silicon, +/−0.3 nm.

FIGS. 5A-5F illustrate an example of a cross-sectional view of thestraightening of an etched sidewall surface of a line 510 of crystallinephase material.

FIG. 5A illustrates a cross-sectional view after etching a layer ofcrystalline phase material using a mask element to form the line 510.The line 510 has a sidewall surface 504, represented by a dashed line inthe Figure, having a roughness defined by the atoms arranged in acrystal lattice within the line 510. The type of crystal lattice dependson the material of the line 510. In one embodiment, the atoms aresilicon atoms arranged in a diamond cubic crystal structure. Materialshaving other types of crystal lattices structures may alternatively beused.

As shown in FIG. 5A, the sidewall surface 504 includes kink sites whichdefine the roughness of the sidewall surface 504. A kink site is alocation along the sidewall surface 504 where two or more atoms in thecrystalline phase region 510 may be bonded with a single atom. Forexample, kink site 520 is the location where atom 522 and atom 524 maybe bonded together by a single atom. The kink sites are energeticallyfavorable sites for crystalline growth because it is more difficult tobond an atom on an already flat crystal surface. An atom which bonds toa flat surface will include several dangling bonds, which causes thetotal energy of the atom to be relatively high. In contrast, an atomwhich bonds to a kink site will have less dangling bonds than if it wereto attach to a flat surface, and thus a lower total energy. As a result,during an epitaxial process, atoms will preferentially bond at theseenergetically favorable kink sites, which advances crystalline growthalong a crystal plane of the material of the line 510. This in turncauses the straightening of the sidewall surface 504.

FIG. 5B illustrates a stage in the progression of the straightening ofthe sidewall surface 504 during the epitaxial process. As shown in FIG.5B, an atom 530 provided by the epitaxial process bonds to the atoms 524and 522 in the line 510, thus recrystallizing at the kink site. As canbe seen upon comparison of FIGS. 5A and 5B, this causes a shift in thesidewall surface 504.

FIGS. 5C, 5D, 5E and 5F illustrate further stages in the progression ofthe straightening of the sidewall surface 504 during the epitaxialprocess. As shown in these figures, additional atoms provided by theepitaxial process continue to bond at available kink sites, thus causingthe sidewall surface 504 to advance and straighten.

FIGS. 6A-6D illustrate perspective views of a simulation of thestraightening of sidewall surfaces 602, 604 of an etched line 640 ofcrystalline phase material during an epitaxial process. The sidewallsurfaces 602, 604 define opposing sides of the line 640. The material ofthe line 640 between the sidewall surfaces 602, 604 is not shown in theFigures. The simulation can be made using a simulator such as theSentaurus tools available from Synopsys, Inc. A Lattice Kinetic MonteCarlo model is used for this simulation, and each silicon atom on thesurfaces 602, 604 are shown in FIGS. 6A-6B as a separate sphere.

In this example, the line 640 is etched in a silicon wafer with a (100)orientation. The sidewall surfaces 602, 604 are then straightened alonga surface parallel to a {111} plane during the epitaxial process.

FIG. 6A illustrates a perspective view after etching the layer ofcrystalline phase material using a mask element to form the line 640.FIG. 6B illustrates a stage in the progression of the straightening ofthe sidewall surfaces 602, 604 during the epitaxial process. As can beseen upon comparison of FIGS. 6A and 6B, the epitaxial process causesthe sidewall surfaces 602, 604 to straighten.

FIGS. 6C and 6D illustrate further stages in the progression of thestraightening of the sidewall surfaces 602, 604 during the epitaxialprocess. As shown in these figures, additional atoms provided by theepitaxial process cause the sidewall surface 602, 604 to continue tostraighten.

In this example, FIG. 6B shows the progression one minute afterbeginning the epitaxial process. FIG. 6C shows the progression afterfour minutes, and FIG. 6D shows the progression after ten minutes. Theepitaxial growth and thus the resulting straightening after certainperiods of time depends on the epitaxial process and the correspondingprocess parameters, which can vary from embodiment to embodiment.

FIGS. 6E-6H illustrate top views of the straightening of sidewallsurfaces 602, 604 of an etched line 640 for the respective perspectiveviews in FIGS. 6A-6D.

In this example, the etched line 640 as illustrated in FIGS. 6A and 6Ehas an initial average line width (or critical dimension) of 10.0 nm,and an LWR of 3.09 nm.

After performing the epitaxial process for one minute, the etched line640 as illustrated in FIGS. 6B and 6F has an average line width of 11.2nm, and an LWR of 2.44 nm. After performing the epitaxial process forfour minutes, the etched line 640 as illustrated in FIGS. 6C and 6G hasan average line width of 13.2 nm, and an LWR of 1.73 nm. Afterperforming the epitaxial process for ten minutes, the etched line 640 asillustrated in FIGS. 6D and 6H has an average line width of 15.4 nm, andan LWR of 1.51 nm.

Thus, in this example the epitaxial process causes the LWR of the line640 to be reduced by more than half. The increase in the line widthduring the epitaxial process can be compensated for by reducing the sizeof the mask used to initially etch the line 640, and/or by alsoperforming a subsequent etching process as described below withreference to FIGS. 8-9, so that the straightened line can have thedesired line width.

FIG. 6I is a plot of the simulated width of the line 640 between thesidewall surfaces 602, 604 along the length of the line 640 for thesimulated results shown in FIGS. 6A-H. The initial line width is labeled“CD 0, average=10 nm” in FIG. 6I. The line width after one minute of theepitaxial process is labeled “CD 1, average=11.2 nm”, after four minutesis labeled “CD 2, average=13.2 nm”, and after ten minutes is labeled “CD2, average=13.2 nm”. As can be seen in FIG. 6I, the epitaxial growthprocess acts to suppress the high frequency components of the linewidth.

FIG. 6J is a plot of the simulated LWR versus the thickness of theepitaxial regions formed on the sidewall surfaces 602, 604 during theepitaxial process. As can be seen in FIG. 6J, as the epitaxial processcontinues, which corresponds to an increase in the thickness of theepitaxial regions, the LWR and the average slope of the sidewallsurfaces 602, 604 significantly decreases.

FIG. 7 illustrates an example simulation of the epitaxial growth processfor various surfaces along different planes of a crystal lattice for amaterial having a diamond cubic crystal structure. In this example, thematerial is silicon.

As can be seen in FIG. 7, the roughness of the sidewall surface dependsupon which plane of the crystal lattice the sidewall surface extendsalong. Thus, in some embodiments, the mask element and the materiallayer are arranged such that the straightened sidewall surface extendsalong a surface parallel to the plane of the crystal lattice of thematerial layer which will be the straightest following the epitaxialprocess.

As shown in FIG. 7, the {111} planes are the straightest after theepitaxial process for material having the diamond cubic crystalstructure, the {110} planes are the next straightest, and the {100}planes are the least straight. This variation in the straightness amongthe various planes occurs because a surface along the {111} planes hasthe slowest epitaxial growth rate and a surface along the {100} planeshas the fastest epitaxial growth rate. In other words, on a {111} plane,the probability that an atom will attach to a flat surface is lower thanthe probability that an atom will attach to a flat surface on a {100}plane. Thus, in one embodiment in which the material layer comprises amaterial having a diamond cubic crystal structure, such as silicon, thetop surface of the material layer is along a (110) plane, and thestraightened sidewalls are formed along a {111} plane of the diamondcubic crystal structure.

In the example described above, the epitaxial process was carried out tostraighten the sidewall surfaces extending along the longer sides of anelongated line of material. The techniques described above can also becarried out to simultaneously straighten the sidewall surface along theshorter side (e.g. the end) of the elongated line of material, in orderto sharpen the corners between the longer and shorter sides. Thisresults in a line of material having improved line definition, withstraighter sidewall surfaces and sharper corners at the intersection ofthe sidewall surfaces, than is possible using conventional lithographicetch mask technologies.

The corner rounding radius is the radius of a 90-degree arc of ahypothetical circle having a mean position along the intersectionbetween generally perpendicular sides of a line. As an example, using alithographic process, the corner rounding radius of an etched line canbe greater than 50 nm. Using the techniques described herein to form astraightened line, the corner rounding radius can for example be lessthan 3 nm.

As described above, the roughness of a straightened sidewall surfaceafter the epitaxial process depends on which plane of the crystallattice the sidewall surface extends along. Thus, in preferredembodiments, the pair of sidewall surfaces which define opposing sidesof a line extend along a surface parallel to one plane of the crystallattice of the material layer, and the sidewall surface at the end ofthe line extends along a second surface parallel to another plane of thecrystal lattice of the material layer. In one embodiment in which thematerial layer is a material having a diamond cubic crystal structure,the pair of sidewall surfaces extend along a surface parallel to one ofa {111} plane and a {110} plane of the diamond cubic crystal structure,and the sidewall surface at the end of the line extends along a surfaceparallel to the other of the {111} plane and the {110} plane.

In the examples described above, the epitaxial process was preferablycarried out to form sidewall surfaces of the line of material extendingalong particular planes of the crystal lattice of the material layer 110which are straightened during the process. However, in some devices,other considerations such as stress engineering, carrier mobility, andsurface charges/traps may make it undesirable to implement certainintegrated circuit elements using a line of material oriented alongthese particular planes. For example, certain integrated circuitelements may typically be formed in silicon using a {100} wafer with a<110> transistor direction.

As used herein, a wafer orientation is defined by its normal direction,and currently the {100} family of directions is standard insemiconductor fabrication. Because of crystallographic symmetry, all thespecific directions in the {100} family have the same epitaxial growthand etching properties. Whereas a family of wafer orientation directionsis denoted herein with curly brackets, if a specific direction isreferenced herein, it is enclosed in parentheses, such as (100). Mostmodern lithographic processes orient all transistors such that theirlongitudinal direction is the <110> family of crystallographicdirections. As used herein, the “longitudinal” direction of a transistoris the direction parallel to current flow in the transistor, and the“transverse” direction of a transistor is the direction cross-wise tothe current flow in the transistor. A family of lithographic orientationdirections is denoted with angle brackets, whereas if a specificdirection is referenced herein, it is enclosed in square brackets, suchas [110].

The techniques described herein can also be carried out to form a lineof material that can then be used as an etch mask during the patterningof an underlying layer of material. In doing so, a line having straightedges and sharp corners can be formed in the underlying layer, withoutbeing limited to particular orientations within the underlying layer.This results in the line in the underlying layer having improved linedefinition, while also enabling other factors such as stress effects tobe taken into consideration when determining the orientation of thesidewall surfaces of the line.

Various types of integrated circuit devices, such as FinFET transistors,interconnect lines, memory cells or other small features such asnano-wires, may be implemented using the line in the underlying layer.

In addition, the line may be implemented as part of a mask pattern (orreticle) utilized during manufacturing of subsequent devices. As anotherexample, the line in the underlying layer may be implemented as part ofa nanoimprint master template used to form replica nanoimprint masks,sometimes also referred to as stamps or templates. These replicananoimprint masks are then utilized during nanoimprint lithography tomanufacture subsequent devices. In doing so, straight lines and sharpcorners can be defined in a material layer during the nanoimprintlithography process, without being limited to particular orientations ofthe material layer.

FIGS. 8-9 illustrate stages in a manufacturing process flow of a secondembodiment for straightening an etched sidewall surface of a line ofcrystalline phase material.

A first etching process is performed on the structure illustrated inFIGS. 1A and 1B using the mask element 100 as an etch mask, resulting inthe structure illustrated in the top and cross-sectional views of FIGS.8A and 8B (collectively “FIG. 8”). The first etching process useddepends on the material of the material layer 110, and can vary fromembodiment to embodiment. In one embodiment in which the material layer110 is silicon, the first etching process is performed using reactiveion etching.

The first etching process forms an etched sidewall surface 802 in thematerial layer 110 at a location defined by the sidewall surface 102 ofthe mask element 100. Similarly, the etching process forms an etchedsidewall surface 804 in the material layer 110 at a location defined bythe sidewall surface 104 of the mask element 100. The sidewall surface802 and the sidewall surface 804 define opposing sides of a line 850 ofcrystalline phase material in the material layer 110.

As shown in FIGS. 8A and 8B, the variation in the respective sidewallsurfaces 802, 804 of the mask element 100 are carried through to thesidewall surfaces 802, 804 in the material layer 110. Due toundercutting by the etching process, the sidewall surfaces 802, 804 eachextend a distance beneath the mask element 100 to define the line 850.

As described in more detail below, the mask element 100 and the materiallayer 110 are arranged such that the etched sidewall surfaces 802, 804extend along a surface generally parallel to a specific crystal plane ofthe crystal lattice of the material layer 110. This specific crystalplane has a relatively slow etch rate for a subsequent etching process,as compared to other planes of the crystal lattice. The relatively slowetch rate is then utilized to straighten the etched sidewall surfaces802, 804 along the particular crystal plane during the subsequentetching process.

The specific crystal plane may be the plane of the material of thematerial layer 110 having the slowest etch rate for the subsequentetching process. For example, in silicon, the {111} plane, which isdensely packed and has a single dangling-bond per atom, has asubstantially slower etch rate than other planes for various wet-etchchemistries such as potassium hydroxide (KOH), tetramethylammoniumhydroxide (TMAH) and ethylene diamine pyrocatechol (EDP).

Next, the subsequent etching process is performed on the structureillustrated in FIGS. 8A and 8B to etch away additional material of theetched sidewall surfaces 802, 804, resulting in the structureillustrated in the top and cross-sectional views of FIGS. 9A and 9B(collectively “FIG. 9”). Although not illustrated, the subsequentetching process will generally also remove material from the topsurfaces of the material layer 110 adjacent to the sidewall surfaces802, 804. This may be prevented in some embodiments by covering thehorizontal surfaces by a mask such as an oxide, nitride, carbon or othermaterial that is insensitive to the particular etching chemistry.

The etch chemistry of the subsequent etching process can vary fromembodiment to embodiment. In some embodiments in which the materiallayer 110 is silicon, the subsequent etching process is performed usingKOH, TMAH or EDP.

The subsequent etching process acts to straighten the etched sidewallsurface 802 along a surface parallel to the specific crystal planehaving a relatively slow etch rate, thereby defining a straightenedsidewall surface 902. This straightening occurs through the more rapidremoval of atoms at step or kink sites which define the roughness of theetched sidewall surface 802, as compared to the removal of atoms on analready flat crystal surface along the specific crystal plane. The atomsat the kink sites are removed more rapidly because they include a largernumber of dangling bonds than the atoms on the already flat crystalsurface along the specific crystal plane. As a result, the subsequentetching process causes the straightening of the sidewall surface 902along a surface parallel to the specific crystal plane. Thestraightening depends on the duration and etch chemistry of thesubsequent etching process, the material of the material layer 110, andwhich plane of the crystal lattice the straightened sidewall surface 902extends along.

In one embodiment in which the material layer 110 comprises a materialhaving a diamond cubic crystal structure, such as silicon, the topsurface of the material layer 110 is along a (110) plane. The sidewallsurface 902 is then straightened along a surface parallel to a {111}plane during the subsequent etching process using KOH.

The subsequent etching process also acts to straighten the etchedsidewall surface 804 along a surface parallel to the specific crystalplane, thereby defining a straightened sidewall surface 904. Thestraightened sidewall surface 902 and the straightened sidewall surface904 define opposing sides of a line 940 of crystalline phase material.The line 940 has a line width 945. The line width 945 may be for example15 nm, or less.

As a result of the straightening during the subsequent etching process,the variation in the straightened sidewall surfaces 902, 904 of the line940 can be controlled over a distribution much less than the variationin the sidewall surfaces 102, 104 of the mask element 100. These smallvariations arise because the straightened sidewall surfaces 902, 904have variations dependent upon the selective etching of atoms at step orkink sites, which can be readily controlled. As a result, thesevariations in the straightened sidewall surfaces 902, 904, can becontrolled over a distribution much less than the variations due tophotolithographic processes, or other patterning processes, involved inthe formation of the sidewall surfaces 102, 104 of the mask element 100.This results in the line 940 having improved line definition, withstraighter sidewall surfaces 902, 904, than is possible usingconventional lithographic etch mask technologies.

In some embodiments, the epitaxial process described above withreference to FIGS. 1-4, and the etching process described above withreference to FIGS. 8-9, may both be performed to straighten an etchedsidewall surface of a line of crystalline phase material. In such acase, one of the epitaxial process and the etching process may first beperformed to at least partially straighten the etched sidewall surface.The other of the epitaxial process and the etching process may then beperformed on the at least partially straightened sidewall surface. Suchan approach can result in less overall growth of the feature size of thestraightened line, as compared to only performing the epitaxial process.The epitaxial process and the etching process may also be iterativelyperformed a number of times.

While the present invention is disclosed by reference to the preferredembodiments and examples detailed above, it is to be understood thatthese examples are intended in an illustrative rather than in a limitingsense. It is contemplated that modifications and combinations willreadily occur to those skilled in the art, which modifications andcombinations will be within the spirit of the invention and the scope ofthe following claims. What is claimed is:

1. A method for manufacturing a structure, the method comprising:forming a mask element overlying a layer of crystalline phase material,the mask element having a first sidewall surface; etching the layerusing the mask element as an etch mask, thereby forming a secondsidewall surface in the layer at a location defined by the firstsidewall surface; and processing the etched layer to straighten thesecond sidewall surface.
 2. The method of claim 1, wherein thestraightened second sidewall surface extends along a surface parallel toa particular crystal plane of a crystal lattice of the layer, and theprocessing comprises performing an epitaxial process to grow crystallinephase material on the second sidewall surface.
 3. The method of claim 2,wherein the particular crystal plane has an epitaxial growth rate thatis less than that of one or more other planes of the crystal lattice. 4.The method of claim 3, wherein the particular crystal plane has anepitaxial growth rate that is less than that of all the other planes ofthe crystal lattice.
 5. The method of claim 2, wherein at least belowthe mask element, the layer has a diamond cubic crystal structure, andthe particular crystal plane is a {111} plane of the diamond cubiccrystal structure.
 6. The method of claim 2, wherein the growncrystalline phase material is the same material as that of the layer ofcrystalline phase material.
 7. The method of claim 2, wherein the growncrystalline phase material is a different material than that of thelayer of crystalline phase material.
 8. The method of claim 1, whereinthe straightened second sidewall surface extends along a surfaceparallel to a particular crystal plane of a crystal lattice of thelayer, and the processing comprises performing an etching process thathas an etch rate for the particular plane that is less than that of oneor more other planes of the crystal lattice.
 9. The method of claim 8,wherein the etching process has an etch rate for the particular crystalplane that is less than that of all other planes of the crystal lattice.10. The method of claim 9, wherein at least below the mask element, thelayer has a diamond cubic crystal structure, and the particular crystalplane is a {111} plane of the diamond cubic crystal structure.
 11. Themethod of claim 1, wherein the first sidewall surface has a first lineedge roughness, and the straightened second sidewall surface has asecond line edge roughness that is less than the first line edgeroughness.
 12. The method of claim 11, wherein the first line edgeroughness is greater than 4 nm, and the second line edge roughness isless than or equal to 1 nm.
 13. The method of claim 1, wherein at leastbelow the mask element, the layer has a diamond cubic crystal structure.14. The method of claim 11, the straightened second sidewall surfaceextends along a surface parallel to a {111} plane of the diamond cubiccrystal structure.
 15. The method of claim 1, wherein: the mask elementhas a third sidewall surface; etching the layer using the mask elementfurther forms a fourth sidewall surface in the layer at a locationdefined by the third sidewall surface; and the processing of the etchedlayer further straightens the fourth sidewall surface.
 16. The method ofclaim 15, wherein the second sidewall surface and the fourth sidewallsurface define opposing sides of a line of crystalline phase material.17. The method of claim 16, wherein after the processing, the line ofcrystalline phase material has a line width roughness between the secondsidewall surface and the fourth sidewall surface that is less thanbefore the processing.
 18. The method of claim 16, wherein the line ofcrystalline phase material has a line width roughness between the secondsidewall surface and the fourth sidewall surface that is less than orequal to 1.5 nm.
 19. The method of claim 1, wherein forming the maskelement comprises performing a lithographic process.
 20. The method ofclaim 1, wherein the straightened second sidewall surface extends alonga surface parallel to a particular crystal plane of a crystal lattice ofthe layer, and processing the etched layer to straighten the secondsidewall surface comprises: performing one of an etching process and anepitaxial process to at least partially straighten the second sidewallsurface; and performing the other of the etching process and theepitaxial process on the at least partially straightened second sidewallsurface, thereby straightening the second sidewall surface.
 21. Themethod of claim 1, further comprising etching a second layer underlyingsaid layer using the straightened second sidewall surface as an etchmask, thereby forming a third sidewall surface in the second layer at alocation defined by the straightened second sidewall surface in saidlayer.
 22. A method for manufacturing a structure, the methodcomprising: forming a mask element overlying a layer of material, themask element having a first sidewall surface, and wherein the layer ofmaterial has anisotropic properties when subjected to a particularprocess; etching the layer using the mask element as an etch mask,thereby forming a second sidewall surface in the layer at a locationdefined by the first sidewall surface; and subjecting the etched layerto the particular process to straighten the second sidewall surface.